We compare to the opacity used by [1]}. (See also the discussion of their work in Section REF .) They took the ISM opacity in the \(V\)  band
\(\kappa _V=107\)  cm\(^2\)  g\(^{-1}_{\textrm {gas}}\) 
\(\kappa _V=107\)  cm\(^2\)  g(gas)\(^{-1}\) 
from [2]}For comparison, the commonly used law of [3]} gives an opacity only 10 % smaller than in [2]}. assuming \(f_{\textrm {d/g}}=0.01\)  and a mean molecular weigth \(\mu =2.353\) , and used the ISM dust extinction law from [5]} with \(R_V=3.1\)  (E. Sanchis 2020, priv. comm.) to scale to other bands up to \(K\) , and the one from [6]} for longer wavelengths. Doing this for H \(\alpha \) , we obtain \(\kappa _{\mathrm {dust,\,H}\,\alpha }=88\)  cm\(^2\)  g\(^{-1}_{\textrm {gas}}\) .
This is much higher than the upper range of our suggested values. Nevertheless, the intrinsic opacity (cross-section per gram of dust) is similar to that of some of our curves.
